The present invention relates in general to seal construction and in particular to a new and useful seal element for flange connections, comprising a plastically deformable seal ring with a support ring associated therewith.
Seal elements are known in a variety of designs. Particular importance has been attached to seals in the form of plastically deformable metal rings, particularly for sealing under conditions of high temperature, for example, ultra-high vacuum seals which must be heated. It is known, however, that plastically deformable seal rings have the disadvantage that in most instances they can be used only once. Then, they are so severely deformed that they do not provide satisfactory sealing in further use. Especially in ultra-high vacuum apparatus where gold wire seal rings are frequently employed, re-use is a significant consideration for reasons of economy.
German Pat. No. 1,959,561 discloses a method of repeatedly using a seal element comprising a seal ring of a plastically deformable material, providing that at every re-use, the seal ring is inserted into the receiving groove in upside down position. In a simple embodiment, this prior art method requires unequal (asymmetric) flanges, which is a considerable disadvantage in practice. The cited patent does provide that, with parts to be sealed which are shaped symmetrically relative to the sealing plane, the asymmetry of the receiving groove is obtained by inserting a special centering ring having a side surface inclined relative to the sealing plane. However, there is still the disadvantage that the flange surface cannot be smooth, they must both be provided with a corresponding groove.
Another problem arising with plastically deformable seal rings particularly in the ultra-high vacuum technique is that even if used only once in connection with a heating process, such a seal may not remain tight, i.e., it is tight during the temperature increase but frequently becomes loose as the temperature decreases again. This may be explained by considering that during the heating the flanges to be connected to each other expand so that the plastic seal ring is subjected to high pressure and deformed, and then as the flanges cool down they reassume their initial size while the seal rings remain deformed. This may result in gaps, thus gas conducting bridges between the sealing surfaces.